Q27. Two guns were fired from the same place at an intervalof 13 minutes but a person in a train approaching theplace hears the second report 12 minutes 30 secondsafter the first. Find the speed of the train in kmph,supposing that sound travels 330 metres per second.

Solution

Let the guns be located at a point say A and the approaching person hear the first report of the gun at point B and the second report at point C.( You should draw this on a piece of paper to understand this further)

If the person were stationary at point B, i.e. the point where he hears the first report , he would hear the second report exactly after 13 minutes.

But he has moved to point C and he has been moving for 12 minutes and 30 seconds to reach point C from point B. Where as the sound reaches the point B after 13 minutes, i,e, 30 seconds more that the time it takes to reach the point C.

Thus we can conclude that the time taken by the man on the motorcycle to travel from B to C is 12 minutes and 30 seconds while the sound wil take exactly 30 seconds to travel the same distance

Q4 DSFind the distance ‘d’ that Ravi coversI. If he walks at 5 km/hr to reach the destination 7 minuteslate. However, had he walked at 6 km/hr, hewould have reached the destination 8 minutes earlier.II. Walking 4/5 of his usual speed, he reached the destination12 minutes late.

SolutionNo when considering the second statement alone - do not assume any value that is provided from statement 1. Thus the question can be answered by statement 1 alone but not by statement 2 alone.Thus answer to this question should be A